*Article* **Comparative Study of Salivary, Duodenal, and Fecal Microbiota Composition Across Adult Celiac Disease**

**Simona Panelli 1,2, Enrica Capelli 2,3, Giuseppe Francesco Damiano Lupo 2,3,4, Annalisa Schiepatti 5, Elena Betti 6, Elisabetta Sauta 7, Simone Marini 3, Riccardo Bellazzi 3,7, Alessandro Vanoli 8, Annamaria Pasi 9, Rosalia Cacciatore 9, Sara Bacchi 2,3, Barbara Balestra 10, Ornella Pastoris 10, Luca Frulloni 11, Gino Roberto Corazza 6, Federico Biagi 5 and Rachele Ciccocioppo 11,\***


Received: 29 February 2020; Accepted: 10 April 2020; Published: 13 April 2020

**Abstract:** Background: Growing evidence suggests that an altered microbiota composition contributes to the pathogenesis and clinical features in celiac disease (CD). We performed a comparative analysis of the gu<sup>t</sup> microbiota in adulthood CD to evaluate whether: (i) dysbiosis anticipates mucosal lesions, (ii) gluten-free diet restores eubiosis, (iii) refractory CD has a peculiar microbial signature, and (iv) salivary and fecal communities overlap the mucosal one. Methods: This is a cross-sectional study where a total of 52 CD patients, including 13 active CD, 29 treated CD, 4 refractory CD, and 6 potential CD, were enrolled in a tertiary center together with 31 controls. A 16S rRNA-based amplicon metagenomics approach was applied to determine the microbiota structure and composition of salivary, duodenal mucosa, and stool samples, followed by appropriate bioinformatic analyses. Results: A reduction of both α- and β-diversity in CD, already evident in the potential form and achieving nadir in refractory CD, was evident. Taxonomically, mucosa displayed a significant abundance of *Proteobacteria* and an expansion of *Neisseria*, especially in active patients, while treated celiacs showed an intermediate profile between active disease and controls. The saliva community mirrored the mucosal one better than stool. Conclusion: Expansion of pathobiontic species anticipates villous atrophy and achieves the maximal divergence from controls in refractory CD. Gluten-free

diet results in incomplete recovery. The overlapping results between mucosal and salivary samples indicate the use of saliva as a diagnostic fluid.

**Keywords:** celiac disease; enteropathy; microbiota; gluten; therapy
